Many types of weatherstrip material exist, and a great variety of different types of weatherstrip materials have been provided in the past. Also, the patent literature is replete with different types of weatherstrip among which may be mentioned the Schlagel et al U.S. Pat. No. 2,228,368; Spraragen U.S. Pat. No. 2,232,570; Balfe U.S. Pat. No. 2,336,835; Merrill U.S. Pat. No. 2,475,332 and Olson U.S. Pat. No. 4,064,654. Of these, the Olson U.S. Pat. No. '654 is of the general type especially constructed for slidable closures, retained in a confining channel in one element with a contact surface projecting therefrom for sliding engagement with a second element.
The Gerald Kessler U.S. Pat. Nos. 3,535,824 and 3,685,206 disclose low friction abrasion resistant plastic weatherstrips of the same general type. More recently, all-plastic weatherstrips have appeared on the market having a rigid base and a flexible generally cylindrical sealing portion projecting therefrom, in some cases the upper surface of the sealing portion being coated with a low friction material. The upwardly projecting sealing portion is generally configured as a circular cylinder and may be either hollow or filled, such as with sponge material. While the circular cylindrical configuration provides a good sealing function and the low friction coating when present provides the advantages of the aforementioned Kessler patents, these new constructions suffer from a serious disadvantage.
Thus, even those new constructions which are provided with a low friction coating have a tendency to crease, "gather" or bunch-up when a mating surface is moved longitudinally thereagainst, e.g. when a weatherstripping material of this type is used in a horizontal slider window or a patio door or the like. As a result, the sealing efficiency of the weatherstrip material becomes reduced and, moreover, friction increases and it becomes increasingly difficult to slide open the window or door.